This invention relates to a pneumatic conveyor of adjustable conveyance capacity for powdered to granular bulk material, particularly for the spray-coating of articles, in which the bulk material is drawn from a storage container by a stream of propellant gas in a pneumatic conveyor and is blown into a conveyor conduit, and in which a pressure regulator is contained in the propellant-gas conduit.
The invention further relates to a pneumatic conveyor system of adjustable conveyance capacity for powdered to granular bulk material, particularly for the spray-coating of articles, in which the material is drawn from the storage container by a stream of propellant gas in a diffuser of a pneumatic conveyor and is blown into a conveyor conduit and in which furthermore a conduit for control gas discharges into the vacuum region of the diffuser so that by the feeding of control gas the vacuum in this region and thereby the conveyor output can be varied, and in which a device for adjusting the feed of control gas is contained in the control-gas conduit.
The invention also relates to a pressure regulator which is particularly suitable for pneumatic conveyor devices for the spray coating of articles.
A pneumatic conveyor device of this type and a pneumatic conveyor apparatus for it, the latter being also referred to as injector or diffuser, are knwon from German Pat. No. 1,266,685.
A spray device for the spray coating of articles to which bulk material can be fed by a pneumatic conveyor system of the type indicated is known from Swiss Pat. No. 429,517.
Furthermore from German Unexamined Application for Pat. No. 26 02 844 a pressure regulator is known. However, this regulator cannot be operated remotely. Furthermore due to leakage losses and inaccuracies it is not suitable for the regulating of gas. Therefore it was necessary up to now in the known pneumatic conveyor systems to use, in addition to a pressure reducer also a separate solenoid valve (on-off valve) as well as a pressure gauge. The pressure gauge indicates the pressure value which is to be set on the pressure reducer. Only after this adjustment has been effected is the solenoid valve opened.
Spray coating with known pneumatic conveyor systems has the following disadvantages:
1. The articles which are to be coated in the spray process frequently require a thicker coating in one region than in another region. Since automatic adjustment is not possible with the known systems, coating has heretofore been effected with an average thickness of coating, i.e. in part too thick and in part too thin. Periods of stay of different length of the articles in front of the spray device are not possible since the articles are passed continuously by the transport device through the dryer. If the transport device is allowed to operate intermittently, undesired other disadvantages can result therefrom. PA0 2. If several articles are to be coated one after the other, a large amount of time is necessary for adjustment of the new pressure and conveyance values. PA0 3. Undesired changes in the stream of material conveyed are only noted after the articles in question have already been coated, this resulting in rejects. PA0 4. The known devices deliver the conveyed bulk material continuously. The bulk material which is delivered between the articles to be coated must be drawn off by expensive devices of high suction power, cleaned and returned in metered quantity to the storage container for the bulk material. PA0 5. The gases--normally air--necessary for the transport and adjustment of the quantity of bulk material conveyed are subject to pressure variations which have a detrimental effect, particularly in the form of too thin a coating of the articles, which leads to rejects or to the necessity of recoating, or else in the form of excessively thick coatings which means the use of an unnecessary amount of material and increased expense.